Boric acid and borax are used for the application of glass, boron ferroalloy, chemical industry, glaze, and finishing agent, and from workplaces of the above, boron-containing waste water is discharged. Further, even in a workplace in which a boron compound is not used as a raw material, flue gas desulfurization waste water generated in a power station, smoke cleaning waste water in a garbage incineration plant, leaching waste water from a landfill and the like, for example, often contain the boron compound.
The boron compound is an essential trace element for animals and plants, but, there is a worry that an excessive consumption of the boron compound causes growth inhibition of plants and reproductive inhibition toxicity and impediment of nervous and digestive systems of animals. It has been clear that boron which is contained in a large amount in seawater or ground water is harmful to a living body such that an excessive consumption thereof causes growth inhibition, and there is provided an extremely strict regulation such that an effluent standard of Water Pollution Control Law for boron is 10 mg/L, and a water quality standard as drinking water for boron is domestically 1.0 mg/L or less, and is 0.5 mg/L or less in a WHO guideline.
However, the removal of boron from water is technically difficult, and the removal of boron from various types of boron-containing waste water such as waste water from a thermal power station containing high-concentration boron, and ground water and waste water generated in seawater desalination containing low-concentration boron, is still one of large technical tasks.
Generally, as a method of removing boron from boron-containing water, a coagulation sedimentation method in which boron is removed as an insoluble sediment by calcium hydroxide and aluminum sulfate, an adsorption resin method in which boron is adsorbed and removed by using a boron-adsorbing resin, a reverse osmosis membrane method, an evaporative concentration method, a solvent extraction method and the like are known.
However, in the method of removing boron as the insoluble sediment by adding the calcium compound such as calcium hydroxide and the aluminum compound such as aluminum sulfate, when high-concentration boron-containing water is set as a target, it is required to use a large amount of medical agents for sufficiently removing boron, resulting in that an amount of use of the medical agents and an amount of generation of sludge are both increased. Therefore, a cost of the medical agents is increased, and at the same time, it becomes difficult to perform sludge treatment.
In the boron-adsorbing resin method, in order to treat waste water containing high-concentration boron, a large amount of boron-adsorbing resin is required since an amount of adsorption of boron of the boron-adsorbing resin is small. Further, there is a problem that a frequency of regenerating the adsorbing resin is increased, resulting in that not only a cost of the resin itself but also a cost of medical agent for regeneration required for regeneration treatment is required.
In order to solve these problems, a method in which boron-containing water is treated by combining the coagulation sedimentation method using the aluminum compound and the calcium compound and the adsorption resin method using the boron-adsorbing resin, has been proposed. However, even with this method, there is a need to add a large amount of medical agents, resulting in that the amount of generation of sludge becomes large, and thus it is difficult to perform the sludge treatment.
Therefore, under the present circumstances, a development of boron treatment method capable of efficiently removing boron from boron-containing waste water and reducing an amount of generation of sludge at a time of performing boron treatment, is desired.